Project Summary Transmission of trypanosomiasis by the tsetse fly remains a driver of poverty and disease in sub- Saharan Africa. There is no cure for trypanosomiasis and the most effective means of controlling trypanosomiasis has been to control the tsetse flies that transmit it, which has largely been done by exploitation of the tsetse olfactory system. Specialized tsetse traps and targets have been successful in reducing tsetse populations, and their efficacy is greatly enhanced by the use of attractive odorants. Synthetic tsetse repellents have also been very useful in the control of tsetse-borne disease, particularly in protecting livestock. Despite the reliance on tsetse olfactory cues to control the spread of trypanosomiasis, there is little understanding of the tsetse olfactory system. Here I aim to anatomically and functionally characterize the olfactory system of the savannah tsetse fly Glossina morsitans morsitans. This work will expand our understanding of the G. m. morsitans olfactory system on a genetic and molecular level. In the end, stable control over human and animal trypanosomiasis cannot be achieved without a detailed understanding of the tsetse olfactory system. The main olfactory organ of the tsetse fly is the antenna, which is covered with chemosensory hairs called sensilla. I characterized by electron microscopy the different types of sensilla that cover the surface and line the specialized cavities of the antenna. In order to better understand the molecular basis of olfaction in tsetse we sought to identify members of the G. m. morsitans Olfactory receptor (GmmOr) gene family. I performed bioinformatic analyses on the genome of G. m. morsitans and identified a family of 31 GmmOrs. In situ hybridization against several of the GmmOrs demonstrated expression of GmmOrs in specific subpopulations of olfactory receptor neurons in the antenna. For example, GmmOr42a and GmmOr7a are expressed in sensilla that line the sensory pit ? a specialized cavity of the antenna that I hypothesize mediates host tracking. I aim to determine by In situ hybridization the expression pattern of the remaining 17 GmmOrs that have not been characterized. GmmOrs with validated expression in the antenna will be functionally analyzed using the Drosophila ?empty neuron? system. The empty neuron system is based on a mutant antennal neuron, the empty neuron, that lacks endogenous odorant receptors and that does not respond to odors. GmmOrs can be systematically expressed in the empty neuron, and the odorant response profile that each individual receptor confers can be deduced by electrophysiological analysis. The functional response profiles of GmmOrs may uncover novel attractants and repellants to be used in ongoing trypanosomiasis control strategies.